Apparatus for bending tubes for samall radius bends



Dec. 27, 1960 A. HUET 2,966,197

APPARATUS FOR BENDING TUBES FOR SMALL RADIUS BENDS Filed March 11, 1955 2 Sheets-Sheet 1 'fiND/FE km: 1-

IN VEN TOR.

Dec. 27, 1960 A. HUET 2,966,197

APPARATUS FOR B ING TUBES FOR s BENDS SMALL RA 2 Sheets-Sheet 2 Filed March 11, 1955 United. States Patent APPARATUS FOR BENDING TUBES FOR SMALL RADIUS BENDS Andi- Huet, Paris, France, assignor to Combustion Engineering, Inc., New York, N.Y., a corporation of Delaware Filed Mar. 11, 1955, Ser. No. 493,663

Claims priority, application France Oct. 27, 1948 3 Claims. (Cl. 15340) The present invention relates to metal working and particularly to methods and apparatus for bending metallic tubes particularly to produce return bends.

In prior applications, such as Patent No. 2,689,596,- issued September 21, 1954, applicant has described improved processes for bending pipes to form return bends whose essential particularity resides in that a difference of temperature is created between the part of the pipe near the internal generatrix of the 'bend and the part of the same pipe near the external generatrix of the bend, in such a way that the internal part is always hotter than the external part during the bending operations. Under these conditions the bending, instead of being effected about the center axis of the pipe, as in the known processes, is efiected about, or in the vicinity of, the outermost generatrix of the return bend, so that the radius of curvature of the final bending can be further reduced.

The present invention has for its object an improved bending process and an apparatus applying the principle ust mentioned for bending straight pipes of any diameter without employing a mandrel or other filler.

According to the process which is the subject of the present invention, a straight pipe passes through a bending apparatus of known type, presenting a roller provided with a groove.

According to the improved process which is the subject of the invention, as the curving of the pipe begins to take place on the roller as soon as the pipe starts to wind on 1t, the region of the pipe which will be situated in the vicinity of the internal generatrix or crotch of the final bend is heated to the desired temperature over a small area immediately before the winding of this portion on the roller of the apparatus. This heating is effected in combination with a deepening of the hollow of the roller groove so as to allow the super-thickness of the metal whlch accumulates at this point to settle along the base of the groove.

I The process is effected continuously, that is the operatron of bending is carried out progressively while the heat is applied from one portion of the final crotch area to the next advancing portion.

Thus, there is obtained during the bending a selfforging of the inner and outer walls of the bend, which avoids all deformation of the straight section of the pipe and produces a reinforcement of the walls of the pipe in the crotch region of the final bend, which reinforcement, moreover, decreases progressively from the internal generatrices of the bend to the external generatrix, without the thickness of the tube being at any point substantially less than its original thickness.

The heating operation may be carried out before introducing the pipe into the bending machine, it being possible to carry out the said heating by means of a row of acetylene burners for example, heating the pipe locally immediately before it passes through the bending apparatus.

The starting product may be a straight pipe which is ice heated all around over a certain portion of its length and then placed in a bending machine of known type. During the bending operation, the zone of the pipe located in the vicinity of the external generatrix of the elbow is cooled, at any suitable points. p

The following description referring to the annexed drawings discloses by way of example the manner in which the invention may be carried into efiect.

Figure 1 represents diagrammatically a bending ma-.

chine of known type which is modified for the execution of the process embodying the present invention.

Figure 2 is a section through the bending roller of the apparatus of Figure 1.

Figure 3 is a view analogous to Figure 1 showing the cooling zone of the pipe.

Figure 4 is a section of the bent pipe.

Figure 5 represents a cross section of the machine shown in Figure 1 at the moment the tube is rolled over the roller at Figure 6 is a cross section at double scale by 6-6 of Figure 5.

As will be seen in Figure 1, a straight pipe 10 which is to be bent is disposed in a bending apparatus of known type consisting essentially of a bending roller 11 whose diameter is of the dimensions of the final bend which it is desired to obtain. The pipe 10 is applied in the groove 12 of the roller 11 by two rollers 13 subjected to a pressure exerted in the direction of the arrow F. The groove 12 of the roller 11 is hollowed out, as is seen in Figure 2, under the pipe 10 so as to accommodate an upsetting of the metal in the crotch of the bend. In addition, the cheeks 14 of the roller 11 are sufliciently extended, as will be seen in Figure 2, so as to clamp the pipe 10 over a portion of more than half the circumference of the said pipe.

According to the invention, a heating means is provided consisting for example of a torch 15 whose cone is directed so as to heat the hatched region A corresponding to part of the crotch of the final bend immediately before the instant in which this portion A advances to receive its curvature on the roller 11.

The bending is effected in-the known manner by means of a finger 16 which grips the pipe 10 and the rotation of the roller 11 in the direction of the arrow in Figure 1 brings the finger into the position shown in chaindotted lines insuring the bending of the pipe which assumes the form indicated in chain-dotted lines in Figures 1 or 3.

Immediately after the heating of the region A, it moves away from the cone of the torch and cools or is cooled by contact with the roller 11 or also by specially provided cooling means.

The operation may be effected continuously, that is, the heating and the speed of rotation of the roller 11 are calculated as a function of the diameter and the thickness of the pipe 10 so that the successive regions A located immediately in advance of the point of winding of the pipe on the roller 11 are brought continuously to the desired temperature before they begin to bend.

The important points of the invention, however, are that the heating of the section of tube 10 corresponding to the internal region of the bend is carried out in combination with the pronounced hollow 12 of the groove of bending roller 11 and the drawing of the tube over the roller. In fact, the pronounced hollow 12 permits the super-thickness of the metal accumulating at this point to settle in the base of the groove.

This arrangement is essential for obtaining a bend the internal passage section of which is not decreased. In fact, there is super-thickness of metal in the crotch region of a bend if the tube should be applied against the bottom of the groove of a roller having a diameter equal to that of the tube, because in that case, the super-thickness produced by mere compression would overlap into the internal passage section. With this invention, due to the fact that the softened metal of the internal tube region can spread out and settle in the pronounced groove12 of roller 11, the internal passage section inside the bend tends to take an oval form shown in cross section at a larger scale on Figure 6, and it can be seen that the internal passage section of the bent region, which has this oval form, is not decreased and can even be increased according to the form given to the pronounced hollow 12 of the roller groove. This point is fundamental for the quality of the bend obtained and, in order to be carried out, traction has to be applied to a roller having a pronounced groove.

Elementary mechanical considerations show that, when tube 10 is drawn over a roller 11 with a force F1, a component G of this force F1 acts so as to make the metal flow back towards the bottom 12A of groove 12. In fact, as may be seen in Figure 5 of the drawings, the component of traction F1 exerting itself on tube at the points 10D, where the curvature sets in, is inclined at a small angle in the general direction from which tube 10 is brought in, due to the temporary elongation of tube 10 at the moment of bending. Under these conditions force F1 has a component G directed downwards, as shown on Figures 5 and '6. This component G applies itself to that part 1013 of tube 10 which remains cold, thus being the outside of the bend, and it is sufficient to produce a compressing deformation of this cold part, which is maintained by the cheeks 12B of roller 11 (as can be seen on Figure 6). In fact, component G does not exceed the limit of flexibility of the cold metal in this region and hence does not depress this region. Under these conditions, component G (Figure 6) acts on the cold side walls 10C of the tube in the directions G1, G2, in order to force the softened metal of the hot region 10A back towards the bottom 12A of groove 12 of roller 11. In fact, these components G1, G2 are sufficient to produce a flowing metal in the crotch region of the tube because these parts are sufficiently heated to flow against the base 12A of the groove 12.

Consequently a new technical result is obtained consisting in producing a bent tube the internal passage section or area D of which is maintained and can even be increased, without it being necessary to use sand, a mandrel, or other filler. On the other hand, the progressive and continuous increase of the thickness of the transversal section, from 100 to 10A of the bend, such as shown on Figure 6, is produced without appreciable decrease of the tube thickness in the external section 10B of the bend; this also is an entirely new and not obvious result in comparison with bending apparatus and process as employed before this invention.

These two results are of prime importance for the quality and efliciency of the bend obtained, because they permit a decrease of heat losses in the flow of the fluid which will circulate in the inside of the bend, and, furthermore, will eventually permit operations for narrowing the bend by pressing the two straight branches together; this would be impossible if the bend did not have the regular and progressive changes in thickness as indicated above.

The final bend (Figure 4) is such that there is no flattening of the tube, that is, the internal section 21 presented for the passage of the fluid on the interior of the tube leading to the bend is not diminished. Nor does it present a notable thinning of the wall of the pipe in the external region 22 of the bend (10B in Fig. 6), while the crotch region 25 (10A, Fig. 6) is reinforced by the piling up and flowing of the metal during the bending.

The diflerential heating of the desired region of the pipe may be effected on straight pipe before the pipe enters the machine or at this time as indicated in Fig. 5.

This heating is preferably effected by means of a small row of acetylene burners for example, which will locally heat the region in question of the pipe in a very limited and rapid manner. Immediately after, and before the heat has had time to spread over the entire circumference of the pipe, the pipe is introduced into the machine and bent.

As a variant, after a preliminary heating of the entire region to be bent of the straight pipe, a lowering of the temperature may be brought about in the region E. indicated in Figure 3 by shaded lines. It is the region E which corresponds to the external region 22 of the final elbow that it is desired to obtain. Owing to this lowering of the temperature it is possible to obtain a bend of reduced radius of curvature.

The lowering of the temperature is obtained, for example, by simple sprinkling of the region B while the pipe is subjected to the bending operation or by continuous sprinkling which may occur at the points G1, G2 situated respectively at the outgoing end of the rollers 13 or between these two rollers.

This application is a continuation in part of Serial No. 111,012 filed in my name on August 18, 1949 and now abandoned.

What is claimed is:

1. In apparatus of the type wherein an empty tube is bent by drawing it around a grooved roller, said apparatus having means provided with a groove for engaging and pressing a straight portion of the tube against the roller. means associated with the roller for gripping the tube to draw it over the roller to bend it, and means for heating the portion of said tube which is to form the crotch of the bend in advance of engagement of the tube with the roller; the improvement comprising; a bending roller having a peripherally extending groove having a base and side walls which in section is concavely and continuously tapered inwardly and is of such depth that the space, provided by the combined grooves in said pressing means and roller, is substantially greater than the normal cross-sectional area of the tube so as to provide a free space at the base of the roller groove; the sides of the groove being so spaced and shaped as to receive a tube therein and to come in contact with the cold parts of the tube which, during the drawing of the tube around the roller, enter the inwardly tapered groove and thereby force the hot part of the tube to flow along the sides of the groove down into the base of the groove.

2. In apparatus of the type wherein an empty tube is bent by drawing it around a grooved roller, said apparatus having means for heating the portion of said tube which is to form the crotch of the bend in advance of engagement of the tube with the roller; the improvement comprising; a bending roller having a peripherally extending, continuously tapered groove of a width suitable to receive the tube with convergently inclined side walls merging into a semi-ovoid contour at the base, the groove being of greater depth in the direction from the periphery of said roller towards its axis of rotation than the semi-diameter of the tube and having continuous side surfaces of the groove located in a plane normal to the axis of rotation, and contacting the diameter of the normal circular cross-section of the tube when engaged in said groove, so that said side portions of the groove act to support relatively cold portions of the tube in approximately the region of its diameter; pressing means contacting outer circumferential portions of the tube; and means for drawing the tube around the bending roller, these two last means acting conjointly to urge the heated portion of the tube against the groove periphery so as to cause the heated portion of the crotch of the tube to flow along the sides of the groove and base to conform to the semiovoid section of the groove.

3. A process of forming a bend from an empty tube comprising the steps of: heating the portion of the empty tube that is to form the crotch of the bend to a higher degree than the part of the tube that is to form the outer portion of the bend; drawing the empty tube around a bending roller having a peripherally extending groove of a depth greater than the semi-diameter of the tube; supporting the relatively cold part of the empty tube with side faces of the groove at the side portions of the tube adjacent to the diametral plane which parallels the axis of rotation of the bending roller; exerting forces against the relatively hot part of the empty tube in directions transversely thereof to cause the metal of the heated portion to flow toward and fill the base of the groove and thus cause the crotch of the bent tube to conform to the contour of the groove at its base, while increasing the internal sectional area of the bent tube and providing a thickened portion for the bend in this region without diminishing the internal free area of the tube.

References Cited in the file of this patent UNITED STATES PATENTS Miller Aug. 7, 1900 Smith Aug. 4, 1903 Reynolds Sept. 19, 1905 Brinkrnan Mar. 29, 1910 Silvey Mar. 25, 1919 Kelly July 8, 1919 Miller Apr. 14, 1925 Henderson May 3, 1927 Lowe Mar. 13, 1928 Snell Dec. 20, 1932 Snell Apr. 9, 1935 Johnson Aug. 29, 1944 Linden Dec. 23, 1947 Fuchs May 14, 1957 FOREIGN PATENTS Netherlands Sept. 16, 1942 

